1. Field of the Invention
The present invention relates to a magnetic recording medium and a method for producing the same. More particularly, it relates to a magnetic recording medium which comprises a magnetic layer consisting of a thin layer of ferromagnetic metal material containing cobalt on a substrate and which has a high corrosion resistance, low coefficient of friction and improved operating stability.
2. Discussion of the Related Art
A magnetic recording medium comprising a magnetic layer consisting of a thin layer of ferromagnetic metal material containing cobalt as a main magnetic component is generally produced by applying metal cobalt or an alloy of cobalt on a substrate film by vacuum deposition or sputtering. Although such a magnetic recording medium is especially suitable for high density recording, the surface of the medium is highly susceptible to moist atmospheric corrosion and corroded materials formed on the surface cause a reduction in the good magnetic properties of the medium and/or severe deterioration of its lubricating characteristics.
To improve corrosion resistance of a ferromagnetic metal thin layer containing cobalt, it has been proposed to treat a magnetic recording medium comprising a ferromagnetic metal layer in a high temperature high humidity atmosphere, for example at 70.degree. C., and 80%RH so as to form crystalline Co.sub.3 O.sub.4 on the surface (cf. U.S. Pat. No. 3,460,968).
However by such treatment of the ferromagnetic metal layer in the high temperature high humidity atmosphere, the corrosion resistance and lubricating performance are not satisfactorily improved. If the ferromagnetic metal layer is stored at 60.degree. C., 90%RH for a week, a corroded layer of cobalt (II) hydroxide (Co(OH).sub.2) is formed so that the coefficient of friction of the magnetic recording medium is increased on standing and wear resistance is decreased. Thus, an increase in the coefficient of friction due to the corroded material is not prevented.